1. Field of the Invention
The field of this invention generally relates to footwear, and more particularly to an article of footwear having a system for providing cushioning and support for the comfort of the wearer.
2. Background Art
One of the problems associated with shoes has always been striking a balance between support and cushioning. Throughout the course of an average day, the feet and legs of an individual are subjected to substantial impact forces. Running, jumping, walking and even standing exert forces upon the feet and legs of an individual which can lead to soreness, fatigue, and injury.
The human foot is a complex and remarkable piece of machinery, capable of withstanding and dissipating many impact forces. The natural padding of fat at the heel and forefoot, as well as the flexibility of the arch, help to cushion the foot. An athlete's stride is partly the result of energy which is stored in the flexible tissues of the foot. For example, during a typical walking or running stride, the achilles tendon and the arch stretch and contract, storing energy in the tendons and ligaments. When the restrictive pressure on these elements is released, the stored energy is also released, thereby reducing the burden which must be assumed by the muscles.
Although the human foot possesses natural cushioning and rebounding characteristics, the foot alone is incapable of effectively overcoming many of the forces encountered during athletic activity. Unless an individual is wearing shoes which provide proper cushioning and support, the soreness and fatigue associated with athletic activity is more acute, and its onset accelerated. This results in discomfort for the wearer which diminishes the incentive for further athletic activity. Equally important, inadequately cushioned footwear can lead to injuries such as blisters, muscle, tendon and ligament damage, and bone stress fractures. Improper footwear can also lead to other ailments, including back pain.
Proper footwear should complement the natural functionality of the foot, in part by incorporating a sole (typically, an outsole, midsole and insole) which absorbs shocks. However, the sole should also possess enough resiliency to prevent the sole from being “mushy” or “collapsing,” thereby unduly draining the energy of the wearer.
In light of the above, numerous attempts have been made over the years to incorporate into a shoe means for providing improved cushioning and resiliency to the shoe. These attempts have included using compounds such as ethylene vinyl acetate (EVA) or polyurethane (PU) to form midsoles. However, foams such as EVA tend to either break down over time or do not provide adequate cushioning characteristics.
One concept practiced in the footwear industry to improve cushioning and energy return has been the use of fluid-filled devices within shoes. For example, U.S. Pat. Nos. 5,771,606, 6,354,020 and 6,505,420 teach such devices. These devices attempt to enhance cushioning and energy return by transferring a fluid between the area of impact and another area of the device. The basic concept of these devices is to have cushions containing fluid disposed adjacent the heel or forefoot areas of a shoe which transfer fluid to the other of the heel or forefoot areas. Several overriding problems exist with these devices.
One of these problems is that often fluid filled devices are not adjustable. Physiological variances between people and the variety of activities for which athletic shoes may be worn create the need for adjustment in support. For example, shoes can be made to adjust for the various lengths of feet, but it is impossible for the shoe industry to account for variations in the weight of the wearer. In addition, the same appropriate balance of support and cushioning could change for various activities such as running, biking, or casual walking. Also, athletes, both professional and amateur, may desire different support for different performance levels. For example, an athlete may desire a different support while training than while competing. Consequently, it is desirable to adjust the amount of pressure within the sole.
It has been known to adjust fluids in the sole of footwear. For example, U.S. Pat. No. 4,610,099 to Signori (the Signori patent) shows a shoe having an inflatable bladder in the sole. The Signori patent provides for the bladder to be inflated using a hypodermic needle insertion. While the device shown by the Signori patent allows a user to customize his or her shoe, the off-board inflation mechanism makes it difficult to inflate the bladder on an as needed basis. Unfortunately, the solution is not to simply slap an on-board inflation mechanism to the shoe. To do so creates extraordinary construction problems. Further, the Signori patent does not address how a custom underfoot system would be adapted for performance in the forefoot. Similar devices are disclosed by U.S. Pat. No. 3,120,712 to Menken and U.S. Pat. No. 1,069,001 to Guy.
Another problem with these support systems is the constant need for inflation. When the system is not inflated and the air pressure is at ambient conditions, the system typically provides no support to the foot. Instead, either the system becomes flat such that the foot will feel the shock from the impact of each step or the bladder will become mushy draining the energy of the wearer.
What is desired is a system whereby variable support under the foot is achieved with a conveniently located on-board inflation mechanism, wherein such a support system uses the common anatomical features of the motion of the foot and is resilient enough to support even when not inflated.